Mushrooms in the Waves

© Else C. Vellinga
Original publication: Mycena News, October 2006

For showy mushrooms, woods are the best places to go—you will find colourful fruitbodies, in all kinds of shapes and sizes on the ground, on trees and on dead wood. The underwater world compensates for its lack of mushrooms by producing beautiful fish, corals, sea slugs, squirts, jelly fish (no fungi), and more than the eye can behold.

You wouldn’t look for mushrooms in a tide-pool, would you? However, even in the sea, there are fungi. They may be nothing like the showy terrestrial ones, but nevertheless, there are lots of different groups. Ascomycetes (the group to which Morels and elfin saddles belong) are the great majority, but around ten are basidiomycetes (like the terrestrial chanterelles, boletes, amanitas and conks). What do these marine basidiomycete species look like? One is a smut fungus parasitizing an underwater plant, (a short introduction to smuts appeared in the November 2004 Mycena News). Another, Mycaureola dilseae parasitizes the blades of the red alga Dilsea carnea. The other eight basidiomycete species grow on wood, twigs and planks, bits of mangroves, or on hair.

They’re small—very small; most of them do not reach one mm in diameter. Nia vibrissa is the giant among them, with fruitbodies up to almost a quarter inch. Most form closed, rounded fruitbodies, with the spores inside, so they do not get washed away prematurely by the sea. The fruitbodies are often hairy, a nice way of coping with the frictions of waves and the exposure to different temperatures, and salinities in a subtidal environment.

Only Digitatispora has its spore-bearing cells, the basidia, exposed to the waves. But, its spores are extremely well adapted to transport by water, they are thin and consist of four branches in three dimensions. Apparently, this makes it easier for the spores to adhere to a substrate where they can germinate and live their saprotrophic lives. Many aquatic fungi have similar spores. The spores of Mycaureola are thin, and extremely long—they range from 105 to 118 μm which makes them longer than any other species of basidiomycete (for comparison, spores of your store-bought portobellos, Agaricus bisporus, are 6.5-8.0 μm). They are slightly boomerang shaped, with a shallow angle between the two ends.

The spores of Nia species are little barrels with four long sticks protruding, but Limnoperdon has ellipsoid spores without appendages. And it looks like the spores of Halocypha are still actively shot off from the basidia, though this mechanism has been lost in the other species. It is the same mechanism found on the gills of normal mushrooms (and within the pores of a bolete) that catapults the spores into free space where they can fall and be carried off in air currents. Puffballs and false truffles, where the spores are formed inside the mushroom, have lost this mechanism and the spores either get into the air by puffing or escape by being eaten by small rodents.

Classifying the tiny fruitbodies of marine fungi posed quite a challenge to those who discovered them. For instance, M. dilseae was first thought to be an Ascomycete, because of its flask-shaped fruitbodies with the opening on top. Nia’s spores were interpreted as conidia, thought to have been formed not on basidia, but budded off. It was ten years after its original description before it was shown that it has basidia and that it is a basidiomycete. This proved to be a general pattern— many of these fungi changed placements in a major way. It was quite a different situation than the splitting up and refining we are used to in terrestrial mushroom genera, where Boletus chrysenteron moves back and forth from Xerocomus to Boletus. No, here the changes were between ascomycetes and basidiomycetes.

As is apparent, the shape of their fruitbodies is no indication of how these fungi relate to their terrestrial counterparts. It is the same with puffballs—all the fruitbodies look quite similar, comprising a sac filled with spores, which are adapted to air transport (with thick, brown, hydrophobic spiny walls). Yet some puffballs are boletes (Astraeus, Scleroderma, and Pisolithus), others are Agaricus—relatives (Lycoperdon, Bovista, Calvatia, Tulostoma, and Battarrea), while earth stars form a separate group related to Gomphus and to the stinkhorns. Where morphology is at a loss, molecules pick up the story. The relationships of the marine fungi are now revealed by comparing their DNA sequences with DNA from known species.

In this way, Binder and his co-workers figured out where five of these marine fungi belong (they also included one very rare fresh-water mushroom—one that not only grows under water, but likes that water to be ice cold).

Interestingly, they found that several of the species mentioned above (viz. Nia vibrissa, Halocyphina villosa, and Calathella mangrovei) group together with terrestrial wood-dwelling species with reduced fruitbodies, the so-called cyphelloid species. The fruitbodies of these mushrooms resemble little cups, with the basidia on the inside surface, and a hairy exterior. Lachnella species are examples of this group and representatives occur quite commonly on dead stems and small branches—I find them on the old stems of the ivy in our front yard in Berkeley.

Mycaureola dilseae, a parasite of a red alga, is related to a different group of white spored species, formerly classified with the Tricholomataceae, that includes honey fungi, velvet shanks and the cone-inhabiting Strobilurus trullisatus. Mycaureola forms an independent lineage of reduced, cyphelloid fruitbodies. Once again nature has re-invented the same thing, but always slightly different, as befits the different origins. Like a painter painting the same scene first with water colours, then with oils.

In general these fungi are widespread—distribution patterns running along coasts of both the Atlantic Ocean and the Pacific Ocean are quite common. Some like it a bit hotter than others. And of course, Mycaureola is restricted to the area where its host grows—that red alga is restricted to the area from the Baltic to Portugal.

Most species grow on submerged wood but you go fishing for one with horse hair for bait! In other words, the marine world, though much poorer in species, still offers a wide variety of fungal ecological adaptations to marvel at!

Further reading: